1. Field of the Invention
The instant invention relates to heat exchangers and, more specifically, to glass tube heat exchangers comprising a plurality of glass tubes in substantially parallel relationship and mounted, at their ends, in apertures provided in tube sheets. The invention is particularly concerned with such heat exchangers which further comprise box headers.
2. Description of the Prior Art
U.S. Pat. No. 4,117,884 discloses a glass tube heat exchanger comprising a parallel array of glass tubes mounted, at their ends, in a cast resin or plastic. According to the reference, the conventional tube sheet is obviated by the cast resin or plastic.
U.S. Pat. No. 4,295,522 discloses a glass tube heat exchanger comprising a parallel array of glass tubes mounted in a tube sheet provided with apertures which are larger than the cross-sectional area of the tubes. The tubes are sealed in the tube sheet by a liquid casting resin which, by capillary action, enters the annular gaps between the edges of the tube sheet apertures and the tubes. U.S. Pat. No. 4,224,982 discloses a similar glass tube heat exchanger which additionally includes a protective tube sheet composed of an acid-resistant and heat-resistant material.
U.S. Pat. No. 4,159,035 discloses a tube and tube sheet seal. According to the reference, a resilient sheet is placed on one side of the tube sheet and a tube is used to force a portion of the resilient sheet through an aperture in the tube sheet whereby a portion of the resilient sheet covers the end of the tube. That portion is cut thereby allowing the resilient sheet to contract and form a flange around the outside of the tube.
U.S. Pat. No. 4,317,483 discloses a glass tube heat exchanger and a composite tube and tube sheet seal. The tube sheet is provided with openings having a diameter larger than the exterior diameter of the tubes mounted therein. The seal comprises, on either side of the medial plane of the tube sheet, lips which bear resiliently and substantially tightly against the outer wall of the tube passing through the opening while retaining the tube some distance away from the edges of the opening. In one embodiment, a sleeve is disposed between the tube and the edges of the opening in the tube sheet and rings provided with the lips are screwed onto the sleeve on each side of the tube sheet.
U.S. Pat. No. 3,559,730 discloses a glass tube heat exchanger and, specifically, a seal for securing a glass tube in a tube sheet. According to the reference, interposed between the end of each tube and a tube sheet aperture, there is disposed a "sealing sleeve having at least one and preferably two external sealing zones adapted to seal against the edges of the aperture and at least one external sealing zone adapted to seal against the tube."
None of the prior art references discussed above and, indeed, no prior art of which the applicants are aware, discloses a glass tube heat exchanger, including box headers, which is operable to circulate a liquid through the glass tubes. This is understandable because the prior art does not disclose a tube to tube sheet seal which is capable of withstanding the fluid pressure associated with a liquid-to-fluid glass tube heat exchanger comprising box headers.
Known are liquid-to-fluid glass tube heat exchangers comprising generally U-shaped tube bends. The tube bend is operable to circulate a liquid from one tube to another tube. The use of tube bends, however, necessitates a wide separation between individual tubes so that the tube bends can be installed on the tubes. Box headers obviate tube bends in liquid-to-fluid glass tube heat exchangers. In addition, the use of box headers allows for much smaller tube separation thereby increasing the overall efficiency of heat exchangers incorporating box headers.